The invention relates to a light pipe illuminator. The invention is of particular advantage for use in illumination of dials and knobs.
Faceted light pipes are well known for the illumination and back lighting of liquid crystal displays where a planar surface is back lit by a wedge shaped light pipe having a planar front surface and a faceted back surface. Light is fed into the light pipe and the light travels along the light pipe until it hits a facet whereupon it is reflected towards and through the front surface. The light pipe includes a series of angled facets along its length thus illuminating the whole surface overlying the light pipe.
According to the invention there is provided a light pipe illuminator comprising a looped light pipe defining an endless light path, the looped light path including a substantially planar front surface and a faceted back surface comprising a series of angled facets arranged about the loop and arranged to reflect light towards and through the planar front surface, and at least one light input port along the light path, the walls of the looped light path arranged such that the light entering the light pipe travels about the loop such that the loop is illuminated through out the front surface.
Thus the loop may surround an object which needs to be illuminated rather than having to illuminate a whole surface part of which may lie behind a solid object through which light may not pass.
Once light has entered the light pipe the light travels about the light path by total internal reflection so that the energy required to light such a loop is kept low.
Preferably in order for there to be minimal light losses the loop is annular or partially annular so that it may be used to illuminate round objects such as dials, knobs, etc. This is particularly useful for lighting dials and knobs on an instrument panel of for example a motor vehicle.
In order to effect even light distribution preferably the illuminator includes two light input ports arranged to diametrically opposite regions of the looped light pipe.
The light pipe is typically of a clear acrylic or polycarbonate material.
Preferably the light source comprises light emitting diodes.
It is nor essential that the light rays input into the ports are collimated there may be cases for example when the light path is long for example with a large diameter loop when collimated light will help to ensure that the entire loop is illuminated.
Typically the light path tapers from a maximum cross-section at the light source to a minimum at the next light source.
In such a case preferably the input port includes a light input device in accordance with the applicant""s co-pending application entitled xe2x80x9cLight Input Device for Light Pipe Illuminatorxe2x80x9d. Such a light input device comprises a first convex lens arranged such that its principal focus lies substantially at the light source such that rays of light from the light source after passing through the lens are substantially parallel to the principal axis of the first lens, and an auxiliary light collecting device, extending from the periphery of the first lens, and comprising a plurality of secondary convex lenses, the principal focus of each secondary lens substantially coinciding with the light source and the principal axis of the first lens, each secondary lens producing collimated light at an angle to the principal axis of the first lens, and for each secondary lens, a reflective surface arranged such that collimated light having passed through the secondary lens is reflected to a direction substantially parallel to the principal axis of the first lens.
Typically the depth of the light path is between 1 cm and 5 cm, and the diameter of the curved loop is up to 20 cm.